One of the most common knee injuries is an anterior cruciate ligament sprain or tear.

Athletes who participate in high demand sports like soccer, football, and basketball
are more likely to injure their anterior cruciate ligaments.

If you have injured your anterior cruciate ligament, you may require surgery to regain
full function of your knee. This will depend on several factors, such as the severity
of your injury and your activity level.

Anatomy

Normal knee anatomy, front view

Three bones meet to form your knee joint: your thighbone (femur), shinbone (tibia),
and kneecap (patella). Your kneecap sits in front of the joint to provide some protection.

Bones are connected to other bones by ligaments. There are four primary ligaments
in your knee. They act like strong ropes to hold the bones together and keep your
knee stable.

Collateral Ligaments

These are found on the sides of your knee. The medial collateral ligament is on the
inside and the lateral collateral ligament is on the outside. They control the sideways
motion of your knee and brace it against unusual movement.

Cruciate Ligaments

These are found inside your knee joint. They cross each other to form an "X" with
the anterior cruciate ligament in front and the posterior cruciate ligament in back.
The cruciate ligaments control the back and forth motion of your knee.

The anterior cruciate ligament runs diagonally in the middle of the knee. It prevents
the tibia from sliding out in front of the femur, as well as provides rotational stability
to the knee.

Several studies have shown that female athletes have a higher incidence of ACL injury
than male athletes in certain sports. It has been proposed that this is due to differences
in physical conditioning, muscular strength, and neuromuscular control. Other suggested
causes include differences in pelvis and lower extremity (leg) alignment, increased
looseness in ligaments, and the effects of estrogen on ligament properties.

When you injure your anterior cruciate ligament, you might hear a "popping" noise
and you may feel your knee give out from under you. Other typical symptoms include:

Pain with swelling. Within 24 hours, your knee will swell. If ignored, the swelling
and pain may resolve on its own. However, if you attempt to return to sports, your
knee will probably be unstable and you risk causing further damage to the cushioning
cartilage (meniscus) of your knee.

Physical Examination and Patient History

During your first visit, your doctor will talk to you about your symptoms and medical
history.

During the physical examination, your doctor will check all the structures of your
injured knee, and compare them to your non-injured knee. Most ligament injuries can
be diagnosed with a thorough physical examination of the knee.

Imaging Tests

Other tests which may help your doctor confirm your diagnosis include:

X-rays. Although they will not show any injury to your anterior cruciate ligament, x-rays
can show whether the injury is associated with a broken bone.

Magnetic resonance imaging (MRI) scan. This study creates better images of soft tissues like the anterior cruciate ligament.
However, an MRI is usually not required to make the diagnosis of a torn ACL.

Treatment for an ACL tear will vary depending upon the patient's individual needs.
For example, the young athlete involved in agility sports will most likely require
surgery to safely return to sports. The less active, usually older, individual may
be able to return to a quieter lifestyle without surgery.

Nonsurgical Treatment

A torn ACL will not heal without surgery. But nonsurgical treatment may be effective
for patients who are elderly or have a very low activity level. If the overall stability
of the knee is intact, your doctor may recommend simple, nonsurgical options.

Bracing. Your doctor may recommend a brace to protect your knee from instability. To further
protect your knee, you may be given crutches to keep you from putting weight on your
leg.

Physical therapy. As the swelling goes down, a careful rehabilitation program is started. Specific
exercises will restore function to your knee and strengthen the leg muscles that support
it.

Surgical Treatment

Rebuilding the ligament. Most ACL tears cannot be sutured (stitched) back together. To surgically repair the
ACL and restore knee stability, the ligament must be reconstructed. Your doctor will
replace your torn ligament with a tissue graft. This graft acts as a scaffolding
for a new ligament to grow on.

Grafts can be obtained from several sources. Often they are taken from the patellar
tendon, which runs between the kneecap and the shinbone. Hamstring tendons at the
back of the thigh are a common source of grafts. Sometimes a quadriceps tendon, which
runs from the kneecap into the thigh, is used. Finally, cadaver graft (allograft)
can be used.

There are advantages and disadvantages to all graft sources. You should discuss graft
choices with your own orthopaedic surgeon to help determine which is best for you.

Because the regrowth takes time, it may be six months or more before an athlete can
return to sports after surgery.

Procedure. Surgery to rebuild an anterior cruciate ligament is done with an arthroscope using
small incisions. Arthroscopic surgery is less invasive. The benefits of less invasive
techniques include less pain from surgery, less time spent in the hospital, and quicker
recovery times.

Animation courtesy Visual Health Solutions, Inc.

Unless ACL reconstruction is treatment for a combined ligament injury, it is usually
not done right away. This delay gives the inflammation a chance to resolve, and allows
a return of motion before surgery. Performing an ACL reconstruction too early greatly
increases the risk of arthrofibrosis, or scar forming in the joint, which would risk
a loss of knee motion.

Whether your treatment involves surgery or not, rehabilitation plays a vital role
in getting you back to your daily activities. A physical therapy program will help
you regain knee strength and motion.

If you have surgery, physical therapy first focuses on returning motion to the joint
and surrounding muscles. This is followed by a strengthening program designed to protect
the new ligament. This strengthening gradually increases the stress across the ligament.
The final phase of rehabilitation is aimed at a functional return tailored for the
athlete's sport.

In order to assist doctors in the management of ACL injuries, the American Academy
of Orthopaedic Surgeons has done research to provide some useful guidelines. These
are recommendations only and may not apply to each and every individual case. For
more information: AAOS Clinical Practice Guideline: Management of Anterior Cruciate Ligament InjuriesAAOS Clinical Practice Guideline: Management of Anterior Cruciate Ligament Injuries (http://www.orthoguidelines.org/topic?id=1018).

AAOS does not endorse any treatments, procedures, products, or physicians referenced
herein. This information is provided as an educational service and is not intended
to serve as medical advice. Anyone seeking specific orthopaedic advice or assistance
should consult his or her orthopaedic surgeon, or locate one in your area through
the AAOS "Find an Orthopaedist" program on this website.